As magnetic powder suitable for high-density recording used in a magnetic recording medium, hexagonal ferrite magnetic powder has been known. For example, JP-A-2011-178654 describes hexagonal ferrite magnetic powder that has a small particle size and enhanced magnetic characteristics by adding a rare earth element and Bi.
A magnetic recording medium such as a magnetic tape is demanded to have excellent durability on running on a drive, in addition to favorable magnetic characteristics as a recording medium. JP-A-2011-225417 describes a technique of improving durability of a magnetic recording medium by using hexagonal ferrite magnetic powder having Al coated on the surface thereof.
Associated with the increasing use of digital data in recent years, a magnetic recording medium storing a huge amount of data is demanded to have improved characteristics on both the magnetic characteristics and the durability. It has been considered that it is substantially effective therefor to utilize both the technique for enhancing the magnetic characteristics with the hexagonal ferrite magnetic powder having Bi added thereto as described in JP-A-2011-178654 and the technique for enhancing the durability with the hexagonal ferrite magnetic powder having Al coated thereon as described in JP-A-2011-225417.
As a result of the investigations made by the present inventors, however, it has been found that the SNR (S/N ratio), which is one of the important factors of the magnetic characteristics of the recording medium, is not sufficiently improved only by utilizing the techniques described in JP-A-2011-178654 and JP-A-2011-225417. A magnetic recording medium is undergoing growing demand for SNR for dealing with a high recording density of these days.